1. Technical Field
The present invention relates to a semiconductor device in which both a silicon-on-insulator (SOI) structure and a bulk structure are formed on the same substrate and a manufacturing method thereof
2. Related Art
A field effect transistor (FET) formed on a silicon-on-insulator (SOI) substrate has attracted attention in terms of its availability that it has advantages such as easiness in element's isolation, latch-up free and a small source-drain junction capacitance. Especially, a fully depleted SOI transistor consumes less power and can operate in high speed. In addition, the fully depleted SOI transistor can be easily driven with a small voltage. For this reason, a lot of researches have been carried out in this field.
Separation by Bonding Si Islands (SBSI) for LSI Application (T. Sakai et al, Second International GiGe Technology and Device Meeting, Meeting Abstract, May 2004, Pages: 230-231) is an example of related art. Though bonded substrates and the like have been conventionally used as SOI substrates, the example discloses a method to manufacture a SOI transistor at a reduced cost by forming a SOI structure on a bulk substrate.
According to the aforementioned method, in order to form a SOI structure and a bulk structure on the same substrate, element isolation regions such as a trench structure and a local oxidation of silicon (LOCOS) structure have to be separately formed respectively in the SOI structure and the bulk structure on the semiconductor substrate. This increases the area where the element isolation regions occupy, increasing the size of the chip. Furthermore, the number of the process steps is also increased.